The present invention relates to an inkjet printing device, and a method for controlling the inkjet printing device.
An inkjet printing device is typically provided with a movable carriage mounting a print head, which is provided with arrays of nozzles. The carriage is movable in a direction substantially perpendicular to a sheet feeding direction, and the nozzle arrays extend in the sheet feeding direction. The inkjet printing device is typically controlled such that the sheet and the carriage are alternately driven to move, and the printing head (i.e., the nozzle arrays) is controlled to eject ink to the sheet when the carriage moves, in accordance with print data. Such a printing method is well known as an interlace printing method.
Various improvements for accelerating a printing speed, improving quality of printed image, and the like have been suggested. In an example, in order to accelerate the printing speed, the nozzles arrays are elongated in the sheet feed direction to increase a width of an area where an image is printed by one printing movement of the carriage.
Recently, in order to provide high-quality images, glossy paper is often used as the recording sheet. The glossy paper is not impregnated with ink well and accordingly, black ink does not dry well on the glossy paper. Therefore, when a black image is to be printed on the glossy paper, a printing operation is performed in a color-mixing printing mode, where the color inks other than the black ink, (e.g., cyan, yellow and magenta inks) are overlaid to form a black image.
Even with the above control, image quality will not be improved sufficiently. For example, if the array of nozzles are elongated to accelerate the printing speed, an inclination of the array with respect to the sheet feed direction affect the image quality. In the printing device employing the interlace method, a printed line formed by a nozzle located at one end of the array, and a printed line formed by a nozzle located at the other end of the array should be overlapped. If the nozzle array is inclined with respect to the sheet feed direction, the two printed line formed by the upstream side end nozzle and the downstream side end nozzle may slightly shift with respect to each other in the carriage movement direction, which deteriorates the image quality.
Further, when the printing device performs bi-direction printing operation in the color-mixing mode, control described below is performed.
When the carriage moves in one direction, cyan, yellow and magenta images are printed in this order to form a black image, while when the carriage moves in the opposite direction, magenta, yell and cyan images are printed in this order. Depending on the direction where the carriage moves, the color tone of the black image is slightly different. That is, if the black image is formed with the bi-directional movement of the carriage in the color-mixing mode, the color tone of the entire image becomes uneven. Therefore, when the printing operation is performed in the color-mixing mode, the one-directional movement of the carriage is generally employed.
It should be noted that when the printing operation is performed in the color-mixing mode with the one-directional movement of carriage, since the three color images are formed exactly on the same position on the recording sheet, a higher accuracy in controlling the movement of the carriage is required.
In particular, if the printing operation is performed in the color-mixing mode with the one-directional movement of carriage and if the array of the nozzles is inclined with respect to the sheet feeding direction, an image formed by an upstream side nozzles and an image formed by the downstream side nozzles do not match and the quality of the resultant image becomes relatively low. In order to avoid such a problem, accuracy of parts and assembling accuracy have been improved until the blurred condition as described above becomes inconspicuous. However, due to recent requirement of elongating the array of nozzles, it becomes difficult to achieve the sufficient accuracy in the conventional printing device.